Integrated temperature sensor for discrete semiconductor devices

ABSTRACT

A semiconductor die includes a single power transistor or power diode, a temperature sense diode formed close enough to the single power transistor or power diode to measure an accurate temperature. The temperature sense diode comprises first and second diodes or strings of diodes. A separate integrated circuit is operable to measure first and second voltage drops of both the first and second diodes or strings of diodes using same magnitude currents, and estimate the temperature of the single power transistor or power diode based on the difference between the first and second forward voltage drop measurements. An overall pn junction area of the first diode or string of first diodes is different from an overall pn junction area of the second diode or string of second diodes.

RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 14/329,389 filed on Jul. 11, 2014, the entirecontents of which are incorporated herein by reference.

TECHNICAL FIELD

The instant application relates to discrete semiconductor devices, andmore particularly to measuring the temperature of discrete semiconductordevices.

BACKGROUND

Some discrete power semiconductor devices such as IGBTs (insulated gatebipolar transistors), MOSFETs (metal oxide semiconductor field effecttransistors), JFETs (junction field effect transistors), power diodes,etc. include an integrated polysilicon diode as a temperature sensor. Aknown fixed current is driven through the polysilicon diode and theabsolute forward voltage drop of the diode is measured. Ideally, theabsolute forward voltage drop of the diode decreases linearly withtemperature. Hence, the junction temperature of the diode can bedirectly concluded from the measured forward voltage drop using a knownrelationship between forward voltage drop and diode junctiontemperature. However, production variation inherent in semiconductormanufacturing causes a wide variation in the forward voltage behavior ofpolysilicon diodes. As a result, the accuracy of polysilicon diode basedtemperature sensors is relatively low.

In addition, the resistance of traces inside the semiconductor die(chip) from the external terminal to the polysilicon diode and back tothe terminal increase the error. Current flowing through the diodecreates not only a forward voltage drop across the pn junction of thediode, but also a voltage drop within the traces. Hence, the measureddiode voltage is greater than the actual pn junction voltage. While thesign of the error is known, the absolute magnitude is not, furthercompounding the measurement error.

Furthermore, variations of the test current driven through the diodealso introduce error. For example, if the test current increases e.g.due to temperature changes or lot-to-lot changes of that test circuit,then the forward voltage of the diodes increases and this is erroneouslyinterpret as lower temperature. In view of the above and otherconsiderations such as lower cost and complexity, a more accuratetemperature sensor and temperature sensing technique is desired fordiscrete power semiconductors.

SUMMARY

According to an embodiment of a circuit, the circuit comprises asemiconductor die comprising a discrete semiconductor device and atleast one diode. The circuit further comprises an integrated circuitoperable to measure a first forward voltage drop of the at least onediode under a first test condition, measure a second forward voltagedrop of the at least one diode under a second test condition andestimate the temperature of the discrete semiconductor device based onthe difference between the first and second forward voltage dropmeasurements.

According to another embodiment of the circuit, a semiconductor diecomprises a single power transistor or power diode, at least onetemperature sense diode formed close enough to the single powertransistor or power diode so that a junction temperature of the at leastone temperature sense diode is an accurate representation of thetemperature of the single power transistor or power diode. The at leastone temperature sense diode comprises a first diode or string of firstdiodes, and a second diode or string of second diodes. An integratedcircuit that is separate from the semiconductor die and operable tomeasure a first forward voltage drop of the first diode or string offirst diodes by driving a first known current through the first diode orstring of first diodes, measure a second forward voltage drop of thesecond diode or string of second diodes by driving a second knowncurrent through the second diode or string of second diodes, andestimate the temperature of the single power transistor or power diodebased on the difference between the first and second forward voltagedrop measurements. The first and second driving currents have the samemagnitude. An overall pn junction area of the first diode or string offirst diodes is different from an overall pn junction area of the seconddiode or string of second diodes.

According to an embodiment of a method of determining the temperature ofa discrete semiconductor device included in a semiconductor die thatalso comprises at least one diode, the method comprises: measuring afirst forward voltage drop of the at least one diode under a first testcondition; measuring a second forward voltage drop of the at least onediode under a second test condition; and estimating the temperature ofthe discrete semiconductor device based on the difference between thefirst and second forward voltage drop measurements.

According to an embodiment of a method determining the temperature of asingle power transistor or power diode included in a semiconductor diethat also comprises at least one temperature sense diode formed closeenough to the single power transistor or power diode so that a junctiontemperature of the at least one temperature sense diode is an accuraterepresentation of the temperature of the single power transistor orpower diode, the at least one temperature sense diode comprising a firstdiode or string of first diodes, and a second diode or string of seconddiodes, the method comprises, using an integrated circuit that isseparate from the semiconductor die, driving a first known currentthrough the first diode or string of first diodes under a first testcondition, measuring a first forward voltage drop of the first diode orstring of first diodes under the first test condition, driving a secondknown current through the second diode or string of second diodes undera second test condition, measuring a second forward voltage drop of thesecond diode or string of second diodes under the second test condition,and estimating the temperature of the single power transistor or powerdiode based on the difference between the first and second forwardvoltage drop measurements. The first and second driving currents havethe same magnitude. An overall pn junction area of the first diode orstring of first diodes is different from an overall pn junction area ofthe second diode or string of second diodes.

According to an embodiment of a semiconductor die, the die comprises adiscrete transistor, a first diode or string of first diodes, and asecond diode or string of second diodes. The semiconductor die furthercomprises a first terminal connected to a gate of the discretetransistor, a second terminal connected to a collector or a drain of thediscrete transistor, a third terminal connected to an emitter or asource of the discrete transistor, a fourth terminal connected to ananode of the first diode or string of first diodes, and a fifth terminalconnected to an anode of the second diode or string of second diodes.

Those skilled in the art will recognize additional features andadvantages upon reading the following detailed description, and uponviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The elements of the drawings are not necessarily to scale relative toeach other. Like reference numerals designate corresponding similarparts. The features of the various illustrated embodiments can becombined unless they exclude each other. Embodiments are depicted in thedrawings and are detailed in the description which follows.

FIG. 1 illustrates a schematic diagram of an embodiment of a discretesemiconductor die with an integrated diode-based temperature sensor.

FIG. 2 illustrates a flow diagram of an embodiment of a method ofdetermining the temperature of a discrete semiconductor device based onforward voltage drop measurements for an integrated diode-basedtemperature sensor.

FIG. 3 illustrates a plot diagram showing how temperature of a discretesemiconductor die is determined based on the difference between twoforward voltage drop measurements for the integrated diode-basedtemperature sensor of FIG. 1.

FIG. 4 illustrates a schematic diagram of another embodiment of adiscrete semiconductor die with an integrated diode-based temperaturesensor implemented as a string of diodes having a force and senseterminal.

FIG. 5 illustrates a schematic diagram of yet another embodiment of adiscrete semiconductor die with an integrated diode-based temperaturesensor implemented as two parallel strings of diodes.

FIG. 6 illustrates a plot diagram showing how temperature of a discretesemiconductor die is determined based on the difference between twoforward voltage drop measurements for the integrated diode-basedtemperature sensor of FIG. 5.

FIG. 7 illustrates a schematic diagram of an embodiment of a circuitincluding a semiconductor die with a discrete semiconductor device andan integrated diode-based temperature sensor, and an integrated circuitfor determining the temperature of the discrete semiconductor devicebased on forward voltage drop measurements for the integrateddiode-based temperature sensor.

DETAILED DESCRIPTION

According to embodiments described herein, temperature sensors andtemperature sensing techniques are provided for discrete powersemiconductor devices with high overall accuracy. The temperaturesensors and temperature sensing techniques described herein are lesssusceptible to errors caused by production variation, voltage drop dueto resistances of traces within the die (chip) and/or bond wires and/orconnectors, and current source variations. The temperature sensors andtemperature sensing techniques described herein can be used withdiscrete transistors such as IGBTs, MOSFETs, JFETs, etc. and discretediodes. In the context of the present specification, the term “MOSFET”should be understood as including the more general term “MISFET”(metal-insulator-semiconductor FET). For example, the term MOSFET shouldbe understood to include FETs having a gate insulator that is not anoxide, i.e. the term MOSFET is used in the more general term meaning ofIGFET (insulated-gate field-effect transistor) and MISFET(metal-insulator-semiconductor field-effect transistor), respectively.

FIG. 1 illustrates one embodiment of a semiconductor die 100 with anintegrated temperature sensor for use in sensing the temperature of adiscrete power semiconductor device 102. The discrete powersemiconductor device 102 is illustrated as a discrete IGBT in FIG. 1 formerely illustrative purposes and has a gate (G), collector (C) andemitter (E), but could be a discrete MOSFET or discrete JFET where thecollector is instead a drain (D) and the emitter is instead a source(S), or a discrete diode. In the case of a discrete MOSFET, the MOSFEThas an intrinsic body diode or reverse diode (i.e. anode connected tosource, cathode connected to drain) which is not shown in FIG. 1 toavoid confusion. The term ‘discrete’ as used herein refers to anelectronic component with just one circuit element such as a transistoror diode, other than an integrated circuit. In comparison, an integratedcircuit typically contains hundreds to billions of circuit elements on asingle chip.

The diode-based temperature sensor 104 integrated in the semiconductordie 100 with the discrete power semiconductor device 102 is a singlesense diode 105 according to this embodiment, such as a polysilicondiode, Schottky diode, etc. in close proximity to the discretesemiconductor device 102. In general, the diode 105 can be any type ofdiode that can be integrated with the discrete semiconductor device 102and has a known forward voltage drop (VF) versus temperaturecharacteristic which allows for estimating the diode junctiontemperature (Tj) from the relative difference (delta) between twoforward voltage drop measurements for the diode 105. That is, the diode105 has a defined forward voltage drop to junction temperaturerelationship. The diode 105 is formed close enough to the discrete powersemiconductor device 100 so that the junction temperature (Tj) of thediode 105 is an accurate representation of the temperature of discretepower semiconductor device 102. For example, the diode 105 can beembedded within the power semiconductor device 102, e.g. close to itssurface.

The semiconductor die 100 further includes a first terminal 106 such asa bond pad connected to the gate of the IGBT or the gate of theMOSFET/JFET, a second terminal 108 connected to the collector of theIGBT or the drain of the MOSFET/JFET, a third terminal 110 connected tothe emitter of the IGBT or the source of the MOSFET/JFET, and a fourthterminal 112 connected to the cathode of the temperature sense diode105. Alternatively, the fourth terminal 112 can be connected to theanode of the temperature sense diode 105 and its cathode can beconnected to third terminal 110 (e.g. with the same orientation shown inFIGS. 4 and 5). The terminals 106-112 can be connected to thecorresponding nodes of the discrete semiconductor device 102 and thetemperature sense diode 105 by one or metal layers, doped semiconductorregions, doped polysilicon regions, etc. In other words, ‘connected’ asused herein can mean either a direct electrical connection (nointermediary structures or regions) or an indirect electrical connection(one or more intermediary structures or regions). The semiconductor die100 can also include a fifth terminal (not shown in FIG. 1) connected tothe anode of the temperature sense diode 105. Alternatively, the anodeof the diode 105 can be internally connected to the emitter of the IGBTor the source of the MOSFET/JFET as shown in FIG. 1, or to the anode orcathode of a discrete diode, and the fifth terminal can be omitted.

In each case, the temperature of the discrete semiconductor device 102is determined by measuring the forward voltage drop of the temperaturesense diode 105 under different test conditions and estimating thetemperature of the discrete semiconductor device 102 based on thedifference (delta) between the forward voltage drop measurements. Such arelative forward voltage temperature measurement technique is lesssusceptible to the errors previously described herein, as compared toconventional absolute forward voltage temperature measurementtechniques.

FIG. 2 illustrates an embodiment of a method of determining thetemperature of the discrete semiconductor device 102. The methodincludes measuring a first forward voltage drop (VF1) of the temperaturesense diode 105 under a first test condition (Block 200) and measuring asecond forward voltage drop (VF2) of the diode 105 under a second testcondition (Block 210). In the case of the embodiment of FIG. 1, thefirst test condition involves driving a first known current IF1 throughthe temperature sense diode 105 e.g. via the terminal 110 of thesemiconductor die 100 connected to the anode of the diode 105, and thesecond test condition involves driving a second known current IF2different than IF1 through the diode 105 e.g. via the same die terminal110. The different forward voltage drop measurements Vf1, VF2 can betaken via the terminal 112 of the semiconductor die 100 connected to thecathode of the diode 105.

The temperature of the discrete semiconductor device 102 is thenestimated based on ΔVF=(VF1−VF2) i.e. the difference between the firstand second forward voltage drop measurements (Block 220). The forwardvoltages VF1 and VF2 can be measured in succession via the die terminals110, 112 connected to the anode and cathode of the temperature sensediode 105.

The measurement of the forward voltage drop VF of the temperature sensediode 105 is a relative measurement i.e. ΔVF measurement, where ΔVF isgiven by:

$\begin{matrix}{{\Delta\;{VF}} = {v*\frac{k*T}{q}*\ln\frac{{IF}\; 1}{{IF}\; 2}}} & (1)\end{matrix}$and where:

ν is an emission factor or quality factor

k is Boltzmann constant

q is elementary charge

T is absolute temperature of the diode

According to this relative measurement technique, the measurement resultis significantly less prone to production variation of sense diodes aswell as production variation (and temperature based changes) of currentsources IF, IF1, IF2. The result is a temperature estimate not directlybased on an absolute VF measurement, but rather based on a relative ΔVFcomputation. That is, the forward voltage drop VF of one diode ismeasured twice: once at low current e.g. IF1 and VF1 is measured; andonce at a larger current e.g. IF2 and VF2 is measured. The differencebetween VF1 and VF2 is directly proportional to absolute temperaturemeasured in Kelvin as shown in FIG. 3, where the temperature sense diode105 shown in FIG. 1 is referred to as ‘diode D’ in FIG. 3 (in FIG. 3,IF1 is the larger current and IF2 is the smaller current, hence, VF1 islarger than VF2).

According to equation (1), ΔVF increases linearly with absolutetemperature T i.e. ΔVF=(VF1−VF2)˜absolute temperature T. Also, ΔVF isindependent of saturation current and therefore not prone to errorscaused by production variation. Instead, the current ratio IF1/IF2determines the overall accuracy of the diode-based temperature sensor.The forward voltage drop difference ΔVF can be directly used to estimatethe temperature of the discrete semiconductor device 102. In the case ofthe diode-based temperature sensor 104 including a single temperaturesense diode 105 as shown in FIG. 1, the resulting signal magnitude issmall. For example, ΔVF/ΔTemperature<1 mV/Kelvin for a singlepolysilicon diode, and more typically between 0.2 to 0.4 mV/K. Toincrease the signal magnitude, the diode-based temperature sensor caninclude more than one diode.

FIG. 4 illustrates another embodiment of the diode-based temperaturesensor 104 for use in sensing the temperature of a discrete powersemiconductor device 102. The embodiment shown in FIG. 4 is similar tothe embodiment of FIG. 1. However, the diode-based temperature sensor104 includes a single string of diodes 300. FIG. 4 shows four diodes inthe diode string 300 for purely illustrative purposes. In general, if“n” diodes are connected in series (i.e. in a string), then the voltagedifference increases to n*ΔVF. Also according to this embodiment, thesemiconductor die 100 has separate force and sense terminals 302, 304for driving the test currents IF1 and IF2 through the string of diodes300 and measuring the corresponding forward voltage drops VF1 and VF2,respectively. Forward voltage drop VFx is measured between terminals 304and 110 while current IFx is driven into terminal 302.

In general, the gain or sensitivity (measured in mV/Kelvin) of thediode-based temperature sensor 104 depends upon the ratio IF1/IF2 of thetest currents and typically ranges between about 0.2 and 0.4 mV/K. Thisis compared to conventional temperature sensors which have a gain orsensitivity that ranges between 1.4 and 1.6 mV/K. The accuracy (error)of the temperature sensor 104 is determined by ln(IF1/IF2). Theexpression ln(IF1/IF2) assumes the same pn junction area for the firstand second forward voltage drop measurements VF1 and VF2. In the case ofthe temperature sensor 104 including two diode strings for measuring VF1and VF2, the current density is relevant. Hence, ln(JF1*Area1/JF2*Area2)is a more general expression where ‘Area1’ denotes the pn junction areaof the first string of diodes and ‘Area2’ denotes the pn junction areaof the second string of diodes (e.g. as shown in FIG. 5). Hence for thesame pn junction area, ΔVF can be expressed by ln(JF1/JF2).

FIG. 5 illustrates yet another embodiment of the diode-based temperaturesensor 104 for use in sensing the temperature of a discrete powersemiconductor device 102. The embodiment shown in FIG. 5 is similar tothe embodiments of FIGS. 1 and 4. However, the temperature sensor 104includes two strings of diodes 400, 402 for estimating the temperatureof the discrete semiconductor device 102 instead of one diode string(FIG. 4) or a single diode (FIG. 1). Each diode string 400, 402 has morethan one diode in FIG. 5. In general, each diode string 400, 402 caninclude one or more diodes in series. In general, there are two paralleldiodes (or two strings of diodes) and IF1 and IF2 can flowsimultaneously. As such, ΔVF can be measured immediately and readdirectly. The measuring process can be performed fast, even using simpleand low-cost (analog) circuits. Even processing such as comparing ΔVF(=Temp) to a threshold to determine whether a temperature threshold isreached (e.g. an over temperature warning threshold or an overtemperature turn off threshold) can be done immediately and with littleadditional circuitry. In contrast, in FIG. 1, IF1 and IF2 flowsequentially, and thus, VF1 is measured first, digitized, memorized andafterwards VF2 can be measured, digitized, memorized and finally ΔVF canbe calculated as previously described herein.

The semiconductor die 100 can include a separate terminal (not shown inFIG. 5) connected to the cathode (CA1, CA2) of each diode string 400,402. Alternatively, the cathode of each diode string 400, 402 can beinternally connected to the emitter of the IGBT or the source of theMOSFET/JFET as shown in FIG. 5, or to the anode or cathode of a discretediode, and this additional terminal can be omitted. Further according tothis embodiment, the anode (A1, A2) of each diode string 400, 402 isconnected to a different terminal 404, 406 of the semiconductor die 100for driving test currents through the diode-based temperature sensor104. The temperature of the discrete power semiconductor device 102 isdetermined by measuring a first forward voltage drop (VF1) responsive toa first current (IF1) driven through the first diode string 400 via thecorresponding die terminal 404, measuring a second forward voltage drop(VF2) responsive to a second current (IF2) driven through the seconddiode string 402 via the corresponding die terminal 406, and estimatingthe temperature of the discrete semiconductor device 102 based on thedifference between VF1 and VF2.

Forward voltage VF1 can be measured via the die terminals 404, 110connected to anode A1 and cathode CA1 of the first diode string 400.Forward voltage VF2 can be measured via the die terminals 406, 110connected to anode A2 and cathode CA2 of the second diode string 402. Inone embodiment, the first current IF1 is driven through the first diodestring 400 simultaneously with the second current IF2 being driventhrough the second diode string 402. The difference between VF1 and VF2can be evaluated in real time and without having to store VF1 and VF2,in order to estimate the temperature of the discrete semiconductordevice 102. This way, memory and digital circuitry are not necessarilyneeded but may be provided if desired. Also, there is no time delay i.e.a real time temperature measurement is available at any single instant.IF1 and IF2 can be driven simultaneously as previously described herein.However, the power semiconductor device 102 itself(IGBT/MOSFET/JFET/diode) may be turned off at that time i.e. no currentthrough the second terminal 108, no significant current through thethird terminal 110 (except small IFx). Normally in power electronicscircuits, the power semiconductors turn on and off periodically withseveral kHz to several MHz. If the VFx measurements are conducted duringthe off-periods, sources of errors are further minimized.

The equation ln((JF1*Area1)/(JF2*Area2)) previously described hereinprovides an option to further tune ΔVF by means of a different pnjunction area for diode strings 1 or 2. Different test currents IF1≠IF2can be obtained by using JF1≠JF2 for the same pn junction area, or byusing JF1=JF2 and Area1≠Area2 and different combinations of both ‘JF’and ‘Area’. In one embodiment, the pn junction area of the first diodestring 400 is different than the pn junction area of the second diodestring 402. According to this embodiment, the first current (IF1) driveninto the first diode string 400 can be the same as the second current(IF2) driven into the second diode string 402. In another embodiment,the first and second diode strings 400, 402 have the same pn junctionarea and IF1≠IF2. In this case, the first current (IF1) driven into thefirst diode string 400 has a different magnitude than the second current(IF2) driven into the second diode string 402. In either case, VF1≠VF2and the junction temperature of the diode-based temperature sensor 104is proportional to ΔVF=VF1−VF2. That is, the difference between VF1 andVF2 is directly proportional to absolute temperature measured in Kelvinas shown in FIG. 6, where the first diode string 400 is referred to as‘D1’, the second diode string 402 is referred to as ‘D2’, IF1≠IF2, andArea1=Area2.

The temperature sense diode, or string of temperature sense diodes, orsense diodes, or strings of temperature sense diodes described herein,are integrated in the semiconductor die 100 and thermally coupled withthe discrete semiconductor device 102 so that the junction temperatureof the diode-based temperature sensor 104 is an accurate representationof the temperature of discrete semiconductor device 102. The diode-basedtemperature sensor 104 can be electrically isolated from the discretesemiconductor device 102 i.e. neither the anode nor cathode areelectrically connected to any nodes (gate, collector/drain,emitter/source, anode, cathode) of the discrete device 102. Instead, theanode and cathode of the diode-based temperature sensor 104 areelectrically isolated from the discrete device nodes 102. Alternatively,the anode or cathode or sense or force terminal of the diode-basedtemperature sensor 104 can be electrically connected to one or more ofthe discrete device nodes, for instance to the emitter terminal of adiscrete IGBT or the source terminal of a discrete MOSFET/JFET, or tothe anode or cathode of a discrete power diode. Such an internalarrangement reduces cost and complexity (the terminal/pad count of thedie is reduced, the number of bond wires is reduced, the pin count ofthe package or module is reduced). For example, a single temperaturesense diode can be integrated with a discrete semiconductor device 102and the anode of the diode can be electrically connected to the emitterof a discrete IGBT or the source of a discrete MOSFET/JFET e.g. as shownin FIG. 1. In another example, a single string of two or moretemperature sense diodes in series can be electrically connected to theemitter of a discrete IGBT or the source of a discrete MOSFET/JFET,where the temperature sensor has separate force and sense terminals,e.g. as shown in FIG. 4. In yet another example, two strings oftemperature sense diodes, each having one or more diodes in series, canbe electrically connected to the emitter of a discrete IGBT or thesource of a discrete MOSFET/JFET e.g. as shown in FIG. 5.

FIG. 7 illustrates an embodiment of a circuit that includes asemiconductor die 100 comprising a discrete semiconductor device 102 anda diode-based temperature sensor 104, and an integrated circuit 500 forestimating the temperature of the discrete semiconductor device 102based on forward voltage measurements for the diode-based temperaturesensor 104. The discrete power semiconductor device 102 is illustratedas a discrete IGBT in FIG. 7 for merely illustrative purposes and has agate (G), collector (C) and emitter (E), but could be a discrete MOSFETor discrete JFET where the collector is instead a drain (D) and theemitter is instead a source (S), or a discrete diode. Depending on thedie technology, different types of parasitic devices P1, P2 can bepresent. The resistance of the transistor drift zone (R_(DRIFT)) andbody (R_(BODY)) are also shown in FIG. 7.

The integrated circuit 500 for estimating the temperature of thediscrete semiconductor device 102 can be implemented as a standalonecircuit separate from other circuitry that controls the normalfunctional operation of the discrete semiconductor device 102.Alternatively, the integrated circuit 500 can be an integral part of thecircuitry that controls the operation of the discrete semiconductordevice 102. For example, the integrated circuit 500 can be implementedas part of a controller or driver programmed or designed to control thenormal functional operation of the discrete semiconductor device 102 andto also estimate the temperature of the discrete semiconductor device102 based on forward voltage measurements for the diode-basedtemperature sensor 104. The integrated circuit 500 includes an analysisunit 502 for measuring a first forward voltage drop VF1 of thediode-based temperature sensor 104 under a first test condition,measuring a second forward voltage drop VF2 of the diode-basedtemperature sensor 104 under a second test condition, and estimating thetemperature of the discrete semiconductor device 102 based on thedifference between VF1 and VF2 as previously described herein.

According to the embodiment shown in FIG. 7, the diode-based temperaturesensor 104 includes two temperature sense diodes DP1, DP2 integratedinto the semiconductor die 100 (e.g. a power transistor die or a powerdiode die). The integrated circuit 500 has a first current source 504for generating a first current IF1 and a second current source 506 forgenerating a second current IF2. The second current source 506 ismatched to the first current source 504 in that the ratio of IF1/IF2 haslittle temperature variation and also little lot-to-lot variation (i.e.very little IF/IF2 spread over production). In one embodiment, thesecond current source 506 is matched to the first current source 504such that the ratio of IF1/IF2 varies by +/−1% or less over atemperature range of −40° C. to 175° C. In general, <1% matching iseasily achievable based on the techniques described herein, even 0.25%,and hence, the temperature measurement is very accurate without majoreffort.

The analysis unit 502 applies current IF1 to a first force terminal (F1)of the semiconductor die 100 and current IF2 to a second force terminal(F2) of the die 100. The first force terminal F1 is connected to theanode of the first temperature sense diode DP1, and the second forceterminal F2 is connected to the anode of the second temperature sensediode DP2. Parasitic resistances RA1, RA2 associated with the respectiveconnection paths are shown in FIG. 7. The semiconductor die 100 alsoincludes first and second sense terminals S1, S2 and a common cathodeterminal C_(D) for measuring forward voltage drops across thetemperature sense diodes DP1, DP2. The cathodes of the temperature sensediodes DP1, DP2 are internally connected within the die 100 to a commonterminal C_(D) of the die 100 in FIG. 7. Alternatively, the cathodes ofthe temperature sense diodes DP1, DP2 can be connected to differentterminals (not shown in FIG. 7) of the die and therefore not internallyconnected within the die 100. In either case, the analysis unit 502measures the forward voltage drop VF1 of the first temperature sensediode DP1 responsive to current IF1 between sense terminal S1 andcathode terminal C_(D) of the die 100. The analysis unit 502 similarlymeasures the forward voltage drop VF2 across the second temperaturesense diode DP2 responsive to current I2 between sense terminal S2 andcathode terminal C_(D) of the die 100. A low ohmic path can be providedbetween the sense terminals S1, S2 of the semiconductor die 100 and theintegrated circuit 500 to ensure accurate sensing. In general, thecurrent through the sense terminals S1, S2 is by default very small,much smaller than IF1 and IF2, and hence, the voltage drop across thelow ohmic path is very small. Also, only ΔVF counts (=VF1-VF2), andhence, as long the current through S1 and S2 is the same, the erroneousvoltage drop in S1 and in S2 cancels out. This is a key quality of therelative measurement techniques described herein, that most errorscancel out.

The analysis unit 502 measures or calculates ΔVF=VF1−VF2, which isdirectly proportional to the absolute junction temperature (Tj) of thetemperature sense diodes (Tj˜ΔVF/Tj˜VF1−VF2). The ΔVF measurement orassessment can be performed inside the same integrated circuit thatincludes the current sources 504, 506. The ΔVF measurement is a relativemeasurement compared to a conventional absolute measurement where thetemperature is estimated based on a single VF measurement. With regardto circuit timing, the current sources 504, 506, the analysis unit 502,the ADC 510, etc. can be synchronized so that the current IFx and the VFmeasurement and calculation, etc. is synchronized with each other. Inaddition, the temperature measurement can be synchronized to theperiodic switching transition of the discrete semiconductor device 102in the case of a discrete IGBT/MOSFET/JFET. The integrated circuit 500can also perform a predetermined action in case a (temperature)threshold is reached, e.g. set a warning flag, increase an errorcounter, turn off the (overheated) discrete semiconductor device 102(e.g. the integrated circuit can be part of a driver IC of the discretesemiconductor device 102), signal an over temperature condition has beenreached to another circuit like a driver IC or DSP/microcontroller, etc.

The integrated circuit shown in FIG. 7 can be adapted for use with anyof the diode-based temperature sensor embodiments described herein. Forexample with regard to the single temperature sense diode embodiment ofFIG. 1, the integrated circuit 500 can include a switch or multiplexer(not shown in FIG. 7 for ease of illustration) for selecting the firstcurrent source 504 to drive test current I1 through the single diode 105and then later selecting the second current source 506 to drive testcurrent I2 through the diode 105. Alternatively, the integrated circuit500 may include a single programmable current source that can beprogrammed to drive two different currents IF1, IF2 through the singlediode 105 at different times. In either case, the analysis unit 502 isat least partly digital in nature and can include memory 508 for storingthe resulting forward voltage measurements VF1, VF. For example, theintegrated circuit 502 can include ADC (analog-to-digital converter)circuitry 510 for converting analog forward voltage measurements tocorresponding digital representations for storage in the memory 508. Theanalysis unit 502 estimates the temperature of the discretesemiconductor device based on the difference between the forward voltagedrop measurements stored in the memory 508 e.g. based on equation (1).In this case of the single temperature sense diode embodiment of FIG. 1,the semiconductor die 100 needs to only have one force terminal and onesense terminal for measuring the forward voltage drops VF1, VF2 aspreviously described herein.

With regard to the single temperature sense diode string embodiment ofFIG. 4, the integrated circuit 500 can have the same or similar designas for the single temperature sense diode embodiment of FIG. 1 in thatthe single string of diodes 300 can be viewed as one diode from theperspective of the integrated circuit 500 with respect to measuring theforward voltage drops VF1, VF2. With regard to the dual temperaturesense diode string embodiment of FIG. 5, the integrated circuit 500 canhave the same or similar design as shown in FIG. 7 in that each stringof diodes 400, 402 can be viewed as one diode from the perspective ofthe integrated circuit 500 with respect to measuring the forward voltagedrops VF1, VF2. In each case, the integrated circuit 500 has arelatively low temperature measurement error.

Spatially relative terms such as “under”, “below”, “lower”, “over”,“upper” and the like, are used for ease of description to explain thepositioning of one element relative to a second element. These terms areintended to encompass different orientations of the device in additionto different orientations than those depicted in the figures. Further,terms such as “first”, “second”, and the like, are also used to describevarious elements, regions, sections, etc. and are also not intended tobe limiting. Like terms refer to like elements throughout thedescription.

As used herein, the terms “having”, “containing”, “including”,“comprising” and the like are open-ended terms that indicate thepresence of stated elements or features, but do not preclude additionalelements or features. The articles “a”. “an” and “the” are intended toinclude the plural as well as the singular, unless the context clearlyindicates otherwise.

With the above range of variations and applications in mind, it shouldbe understood that the present invention is not limited by the foregoingdescription, nor is it limited by the accompanying drawings. Instead,the present invention is limited only by the following claims and theirlegal equivalents.

What is claimed is:
 1. A circuit, comprising: a semiconductor diecomprising: a single power transistor; at least one temperature sensediode formed close enough to the single power transistor so that ajunction temperature of the at least one temperature sense diode is anaccurate representation of the temperature of the single powertransistor, the at least one temperature sense diode comprising: a firstdiode or string of first diodes, and a second diode or string of seconddiodes; an integrated circuit that is separate from the semiconductordie and operable to: measure a first forward voltage drop of the firstdiode or string of first diodes by driving a first known current throughthe first diode or string of first diodes; measure a second forwardvoltage drop of the second diode or string of second diodes by driving asecond known current through the second diode or string of seconddiodes; and estimate the temperature of the single power transistorbased on the difference between the first and second forward voltagedrop measurements, wherein the first and second driving currents havethe same magnitude, and wherein an overall pn junction area of the firstdiode or string of first diodes is different from an overall pn junctionarea of the second diode or string of second diodes, wherein the singlepower transistor is an IGBT having a collector, an emitter and a gate ora FET having a drain, a source and a gate, wherein a cathode of thefirst diode or string of first diodes and a cathode of the second diodeor string of second diodes are directly electrically connected to theemitter of the IGBT or the source of the FET.
 2. The circuit of claim 1,and wherein the semiconductor die comprises a first terminal connectedto the gate of the IGBT or the gate of the FET, a second terminalconnected to the collector of the IGBT or the drain of the FET, a thirdterminal connected to the emitter of the IGBT or the source of the FET,a fourth terminal connected to an anode of the first diode or string offirst diodes, and a fifth terminal connected to an anode of the seconddiode or string of second diodes.
 3. The circuit of claim 1, wherein theintegrated circuit is operable to: store the first forward voltage dropmeasurement; store the second forward voltage drop measurement; andestimate the temperature of the single power transistor or power diodebased on the difference between the stored forward voltage dropmeasurements.
 4. The circuit of claim 1, wherein the at least onetemperature sense diode comprises the string of first diodes and thestring of second diodes.
 5. The circuit of claim 1, further comprising asingle programmable current source that can be programmed to drive thefirst and second known currents.
 6. The circuit of claim 5, wherein theintegrated circuit comprises the single current source.
 7. A method ofdetermining the temperature of a single power transistor included in asemiconductor die that also comprises at least one temperature sensediode formed close enough to the single power transistor so that ajunction temperature of the at least one temperature sense diode is anaccurate representation of the temperature of the single powertransistor, the at least one temperature sense diode comprising: a firstdiode or string of first diodes, and a second diode or string of seconddiodes; the method comprising, using an integrated circuit that isseparate from the semiconductor die: driving a first known currentthrough the first diode or string of first diodes under a first testcondition; measuring a first forward voltage drop of the first diode orstring of first diodes under the first test condition; driving a secondknown current through the second diode or string of second diodes undera second test condition; measuring a second forward voltage drop of thesecond diode or string of second diodes under the second test condition;and estimating the temperature of the single power transistor based onthe difference between the first and second forward voltage dropmeasurements, wherein the first and second driving currents have thesame magnitude, and wherein an overall pn junction area of the firstdiode or string of first diodes is different from an overall pn junctionarea of the second diode or string of second diodes, wherein the singlepower transistor is an IGBT having a collector, an emitter and a gate ora FET having a drain, a source and a gate, wherein a cathode of thefirst diode or string of first diodes and a cathode of the second diodeor string of second diodes are directly electrically connected to theemitter of the IGBT or the source of the FET.
 8. The method of claim 7,wherein the first and second driving currents are each generated by asingle current source.
 9. The method of claim 8, wherein the integratedcircuit comprises the single current source.
 10. The method of claim 7,wherein estimating the temperature of the single power transistorcomprises: storing the first forward voltage drop measurement; storingthe second forward voltage drop measurement; and estimating thetemperature of the single power transistor or power diode based on thedifference between the stored forward voltage drop measurements.
 11. Themethod of claim 10, wherein the at least one temperature sense diodecomprises the string of first diodes and the string of second diodes.12. The method of claim 10, further comprising a single programmablecurrent source that can be programmed to drive the first and secondknown currents.
 13. The method of claim 12, wherein the integratedcircuit comprises the single current source.